The present invention relates to a method for recognizing and differentiating a flow rate error and a dynamic error of an exhaust gas recirculation system (EGR) in the air charge system of an internal combustion engine, an EGR mass flow being measured and modeled indirectly or directly, a measured EGR mass flow signal and a modeled EGR mass flow signal correlated thereto each being compared to one another, and a high-pressure exhaust gas recirculation valve and/or a low-pressure exhaust gas recirculation valve being associated with the air charge system.
The present invention furthermore relates to a computer program product for carrying out the method.
The statutory provisions for onboard diagnosis (OBD) in motor vehicles having internal combustion engines require the recognition of emission-relevant errors in the subsystems of the air charge system. The California legislation thus requires monitoring of the exhaust gas recirculation (EGR) in diesel engines and monitoring of the boost pressure control in gasoline and diesel engines including supercharging, for example, including exhaust gas turbochargers. The European legislation requires the monitoring of the EGR in diesel engines. In the California legislation, inter alia, the recognition of emission-relevant so-called flow errors and also of slow response errors is required. In addition, there is the requirement of locating the cause of a malfunction as exactly as possible, so that defective components may be repaired or replaced.
High/low-flow errors (flow rate errors) are understood as an undesirable response of the EGR, which results in an increase of the exhaust gas emissions up to a value above predefined onboard diagnosis limiting values. A high-flow error refers, for example, to an EGR valve which incompletely closes or jams open. An EGR valve which incompletely opens or jams in the closed state may result in a low-flow error. A slow response error (dynamic error) is understood as a slowed-down response of the exhaust gas recirculation or the boost pressure to a change of the setpoint value. The relevant error scenarios are, for example, a slowed-down EGR valve, a slowed-down exhaust flap, etc.
Both high/low-flow errors and dynamic errors may result in an increase of emissions in, for example, a diesel engine. If the EGR rate is temporarily excessively low due to a low-flow error or a slow response error, it may result in an increased peak combustion temperature and therefore a rise of the nitrogen oxide emissions. A temporarily excessively high EGR rate, in contrast, may result in a reduced combustion temperature and a reduced oxygen excess and therefore in a rise of the soot particle emissions. A temporarily excessively low or excessively high boost pressure may result in disturbances of the air charge of the cylinders, so that the quantity or the time of the fuel injection or the EGR rate is no longer optimally adapted to the actual air charge, which may result in a rise of the exhaust gas emissions.
A flow error has similar effects on the EGR system and the emissions as a slow response error. The high-flow error affects the EGR system and the emissions similarly to a negative slow response error (delayed closing of the EGR valve). The low-flow error has a similar effect as a positive slow response error (delayed opening of the EGR valve) on the EGR system and the emissions.
Various methods exist for the diagnosis of subsystems of the air charge system. For example, some conventional methods monitor the intervention of the charge regulation in the event of a change of the EGR setpoint value. A strong intervention of the charge regulation indicates an undesirable or slow response of the exhaust gas recirculation. Other convention methods model the boost pressure under the assumption of an error-free system and compare the modeled value to the measured boost pressure. If a large difference between the modeled value and the measured value is recognized in the event of a change of the boost pressure setpoint value, this indicates a slow response of the boost pressure control.
A method and a device for carrying out the method for dynamic monitoring of gas sensors of an internal combustion engine are described in German Patent Application No. DE 10 2011 088 296 A1, the gas sensors having a low-pass behavior depending on geometry, measuring principle, aging, or soiling, in the event of a change of the gas state variable to be measured, a dynamic diagnosis being carried out on the basis of a comparison of a modeled signal and a measured signal, and the measured signal being an actual value of an output signal of the gas sensor and the modeled signal being a model value. It is provided that the output signal of the gas sensor is filtered using a high-pass filter and in the event of a change of the gas state variable to be measured, higher-frequency signal components are evaluated. Changes with respect to the dynamics in gas sensors may be detected and quantified using this method.
A related method, as described in German Patent Application No. DE 10 2012 201 033 A1, may be used to ascertain a dead time of gas sensors.
It is an object of the present invention to provide a method which enables a reliable and cost-effectively implemented recognition and differentiation of a flow rate error and a dynamic error of an exhaust gas recirculation (EGR) in the air charge system of an internal combustion engine.
It is furthermore an object of the present invention to provide a computer program product for carrying out the method.